The predominate approach today to introduce factory automated technology into manufacturing is to selectively apply automation and to create islands of automation. The phrase "islands of automation" has been used to describe the transition from conventional or mechanical manufacturing to the automated factory. Interestingly, some appear to use the phrase as though it were a worthy end object. On the contrary, the creation of such islands can be a major impediment to achieving an integrated factory.
Manufacturing examples of islands of automation often include numerically controlled machine tools; robots for assembly, inspection, painting, and welding; lasers for cutting, welding and finishing; sensors for test and inspection; automated storage/retrieval systems (AS/RS) for storing work-in-process, tooling and supplies; smart carts monorails, and conveyors for moving material from work station to work station; automated assembly equipment and flexible machining systems. Such islands are often purchased one at a time and justified economically by cost reductions. An example of an AS/RS system is disclosed in the U.S. Pat. No. 4,328,422 to Loomer. A different type of AS/RS system and control system therefor is disclosed in the U.S. Pat. No. 4,232,370 to Tapley.
To integrate the islands of automation, it is necessary to link several machines together as a unit. For example, a machine center with robots for parts loading and unloading can best be tied to visual inspection systems for quality control. Computer numerical control machine tools can all be controlled by a computer that also schedules, dispatches, and collects data. Selecting which islands to link can be most efficiently pursued on the basis of cost, quality and cycle time benefits.
In some cases, the islands of automation will be very small (e.g. an individual machine or work station). In other cases, the islands might be department-sized. The U.S. Pat. No. 4,611,749 to Kawano discloses the use of robots to transfer parts between such islands which are relatively close to each other.
From a systems viewpoint, islands of automation are not necessarily bad, so long as they are considered to be interim objectives in a phased implementation of an automated system. However, to obtain an integrated factory system, the islands of automation must be tied together or synchronized. Systems synchronization frequently occurs by way of a material-handling system; it physically builds bridges that join together the islands of automation. Early examples of such islands of automation linked together by a material-handling system are disclosed in the U.S. Pat. Nos. 4,369,563 and 3,854,889 to Williamson and Lemelson.
The '563 patent discloses a system including machine tools which perform machining operations on workpieces loaded on pallets. The pallets are delivered to the machine tools from a storage rack by transporters. The workpieces are manually loaded onto the pallets.
The '889 patent discloses a system including work-holding carriers which are selectively controlled in their movement to permit work to be transferred to selected machine tools while bypassing other machine tools.
Automated material handling has been called the backbone of the automated factory. Other than the computer itself, this function is considered by many automation specialists as the most important element in the entire scenario of automated manufacturing. It is the common link that binds together machines, workcells, and departments into a cohesive whole in the transformation of materials and components into finished products. For example, the U.S. Pat. No. 4,332,012 to Sekine et al discloses a control system for assembly lines for the manufacture of different models of automotive vehicles. Temporary storage is provided between assembly steps by a storage section.
To date, one of the major applications for industrial robots has been material handling. Included here are such tasks as machine loading and unloading; palletizing/depalletizing; stacking/unstacking; and general transfer of parts and materials--for example, between machines or between machines and conveyors. An example of one such application is disclosed in the U.S. Pat. No. 4,519,761 to Kenmochi. The '761 patent discloses a combined molding and assembling apparatus wherein a pallet is conveyed by a conveyor. Resin components are carried by the pallet for use in the molding and assembling operation.
Robots are often an essential ingredient in the implementation of Flexible Manufacturing Systems (FMS) and the automated factory. Early examples of the use of robots for assembling small parts is disclosed in the U.S. Pat. Nos. 4,163,183 and 4,275,986 to Engelberger et al wherein robots are utilized to assemble parts from pallets onto a centrally located worktable.
The automated factory may include a variety of material transportation devices, ranging from driver-operated forklifts to sophisticated, computer-operated, real-time reporting with car-on-track systems and color graphics tracking. These material transport systems serve to integrate workcells into FMS installations and to tie such installation and other workcells together for total factory material transport control.
With all of their versatility, robots suffer from a limitation imposed by the relatively small size of their work envelope, requiring that part work fixtures and work-in-process be brought to the robot for processing. Complete integration of the robot into the flexible manufacturing system requires that many parts and subassemblies be presented to the robot on an automated transport and interface system. For example, installation of an assembly robot without an automated transport system will result in an inefficient island of automation needing large stores of work-in-process inventory for support, which are necessary to compensate for the inefficiencies of manual and fork truck delivery.
An example of the use of robots in a manufacturing assembly line is disclosed in the U.S. Pat. No. 4,611,380 to Abe et al.. The '380 patent also discloses the use of a bar code to identify the components to be assembled to a base component to control the assembly operations.
The U.S. Pat. No. 4,616,411 to Suzuki et al discloses a fastening apparatus including a bolt receiving and supply device for use in the automated assembly of a door to a vehicle.
The handling, orienting and feeding of parts as they arrive from vendors are formidable jobs which must be done prior to robotic assembly since, in general, all such parts require reorienting for the assembly robot. The U.S. Pat. No. 4,527,326, to Kohno et al for example, discloses a vibratory bowl which feeds parts to an assembly robot. A vision system enables the robot to properly pick up the parts from the bowl.
Part feeding is a technology that generally has lagged behind the advanced automation system it supports. However, in general, part feeding curtails flexibility, increases costs, increases floor space requirements and lengthens concept-to-delivery time. For maximum flexibility, a minimum amount of tooling should be considered. On the other hand, additional tooling can be used effectively to "buy time" by assisting the robot. Typically, dedicated hardware--bowl feeders, magazines, pallets--is required to feed parts to the robot. Unlike the robot, dedicated hardware is not easily reusable and therefore is less economical for medium-volume applications.
The U.S. Pat. No. 4,383,359 to Suzuki et al discloses a part feeding and assembly system, including multiple stage vibration and magazine feeders. A robot is utilized to change the position of the fed parts for assembly on a chassis supported on a line conveyor. The robot operates in combination with a vision system to reorient the parts.
Neither flexible nor sophisticated, part feeding equipment is usually constructed by highly skilled artisans working with welding torch and hammer in small specialized shops. The most common and most inexpensive feeding method--vibratory bowl feeding--provides the builder with a versatile base easily modified to handle many different parts which are not delicate and which are substantially identical. Delicate parts or parts that tangle, such as motors, are better fed by magazines or trays for exact orientation.
Also, not all parts, for example, can be bowl fed. For most parts, the overriding concern is geometry and, in particular, symmetry. If a part is either symmetric or grossly asymmetric, then vibratory bowl feeding will be easier and more efficient.
Robots may load and unload workpieces, assemble them on the transport, inspect them in place or simply identify them. The kind of activity at the robot or machine and material transport system interface dictates the transport system design requirements. One of the design variables relating to the interface includes accuracy and repeatability of load positioning (in three planes). Also, care in orienting the workpiece when it is initially loaded onto the transport carrier will save time when the work is presented to the robot or the tool for processing. Proper orientation of the part permits automatic devices to find the part quickly without "looking" for it and wasting time each time it appears at the workstation.
Fixtures may be capable of holding different workpieces, reducing the investment required in tooling when processing more than one product or product style on the same system.
The transport system must be capable of working within the space limitations imposed by building and machinery configurations, yet must be capable of continuous operation with the loads applied by a combination of workpiece weight, fixture weight, and additional forces imposed by other equipment used in the process.
The system must also have the ability to provide queuing of parts at the workstation so that a continuous flow of work is maintained through the process. Automatic queuing of transport carriers should provide gentle accumulation without part or carrier damage.
The primary impediment to robotic assembly is economic justification. When the cost of robotic assembly is compared against traditional manual methods or high volume dedicated machinery, robots oftentimes lose out. On one side of the spectrum are the high-volume, high-speed applications where hard automation is used. It's difficult for robots to compete in that environment. On the other side are the low-volume, high variety products that are assembled manually. Robots may lack the dexterity to perform these jobs, and they may cost more than relatively low-paid manual assemblers. There is a middle ground between these two extremes for flexible assembly. Many believe that the best approach is a combination of robots, dedicated equipment and manual assembly.
While assembly is one of the most difficult areas of robotic application, many say it also holds the most promise. Assembly robots offer an array of benefits that cannot be ignored. They can produce products of high and consistent quality, in part because they demand top-quality components. Their reprogrammability allows them to adapt easily to design changes and to different product styles. Work-in-process inventories and scrap can be reduced. Therefore, it is important that the materials transport system serving the robots be capable of quickly moving into position with parts, then quickly moving out of the workstation and on to downstream stations. Prompt transporter movements between stations allow work-in-process inventory to be minimized. Batch sizes are smaller and work faster with only a minimum of queuing at each workstation.
The U.S. Pat. No. 4,594,764 to Yamamoto discloses an automatic apparatus and method for assembling parts in a structure member such as an instrument panel of an automobile. A conveyor conveys a jig which supports the panel to and from assembly stations. Robots mount the parts on the instrument panel at the assembly stations. Robots are provided with arm-mounted, nut-driving mechanisms supplied from vibratory parts bowls.
A link for tying together some of the independently automated manufacturing operations is the automatic guided vehicle system (AGVS). The AGVS is a relatively fast and reliable method for transporting materials, parts or equipment, especially when material must be moved from the same point of origin to other common points of destination. Guide path flexibility and independent, distributed control make an AGVS an efficient means of horizontal transportation. As long as there is idle space and a relatively smooth floor to stick guide wires or transmitters into, the AGVS can be made to go there.
As an alternative to traditional conveying methods, the AGVS provides manufacturing management with a centralized control capability over material movement. Also, the AGVS occupies little space compared with a conveyor line. Information available from the AGVS also provides management with a production monitoring data base. The U.S. Pat. No. 4,530,056 to Mackinnon et al discloses an AGVS system including a control system for controlling the individual vehicles.
Robot installations for transporter interface can be grouped into three principal categories: (1) stationary robots, (2) moving (i.e. mobile) robots (on the floor or overhead), and (3) robots integral with a machine. The moving robots subdivide into two types. First are stationary robots, mounted on a transporter to move between work positions to perform welding, inspection, and other tasks. The second type of moving robot is the gantry unit that can position workpieces weighing more than one ton above the workcells and transport system. The system only has to deliver and pick somewhere under the span of gantry movement.
End effectors used in material handling include all of the conventional styles--standard grippers, vacuum cups, electromagnets--and many special designs to accommodate unusual application requirements. Dual-purpose tooling is often used to pick up separators or trays, as well as the parts being moved through the system.
Vacuum-type grippers and electromagnetic grippers are advantageous because they permit part acquisition from above rather than from the side. This avoids the clearance and spacing considerations that are often involved when using mechanical grippers.
However, the use of vacuum and electromagnetic grippers is not without its problems since cycle time is not just a function of robot speed and its accelerating/decelerating characteristics. Cycle time is dependent on how fast the robot can move without losing control of the load. Horizontal shear forces must be considered in the application of these grippers. This often means that the robot is run at something less than its top speed.
Currently, automotive body assembly utilizes fixtures on which body panels are placed relative to each other in a predefined relative location. The relative location is determined by location points which supports the panel and confines its location to the desired position. Location points are usually comprised of hard stops against which the panels are clamped, or closely confined within acceptable tolerances.
The location points must be adjusted to the correct location relative to adjacent panels and components, within necessary tolerances, before the panels and components are joined by process equipment. To attain the necessary level of accuracy, it is usually necessary to make manual adjustments to the confining clamps by shimming and the like. The adjustment must also be verified by high accuracy measurements. The whole process is very tedious, costly, and time consuming.
When the panel is used as an outside skin for the car body, clamping may mar the outside surface of the panel and harm the final appearance of the car. Such panels are only located in a confined configuration with small clearances. The clearance between the panels and the confining mechanism must be minimized to maintain desired accuracy when allowance is made for panel distortion and mechanism inaccuracies. Manual adjustment and verification is again necessary.
Once the panels are located and clamped or confined to the desired relative positions, the assembly is usually transferred to other process equipment for permanent joining of all panels and components together. Spot welding is a common method of joining in automotive manufacturing. Bonding, fusion, and laser welding are also recognized joining methods of metals and other materials, such as composite polymeric materials.
The integrated subassembly is then unclamped, lifted off the fixtures, and transferred to other assembly locations to be integrated into another subassembly, or finally, the full car body.
Occasionally, robots and programmable devices are used for automating certain automotive body assembly processes such as spot welding and material handling. However, this has not generally extended to the location of the components handled or processed. An example of an exception is disclosed in U.S. Pat. No. 4,944,445. The '445 patent requires the presorting of assembly components and their placement at approximate locations on a specially designed pallet prior to being operated on. This requirement carries with it the inconvenience, cost, and space demands of a multitude of assembly pallets not much different from what is currently experienced with hard automation approaches.
The '445 patent also discloses programmable locators, described as tool carriers, and require that they be fitted with customized tools that are designed to fit the assembly, or the process, such that the assembled parts nest accurately on the tooling jaws.
This arrangement has the advantage over hard automation in that it requires only one set of accurate tooling that remains at the joining station of the parts instead of being duplicated with each pallet as is done with hard automation. However, as many pallets are needed as for hard automation. The locators are arranged in groups with each group constrained to move in common planes of motion, hence limiting flexibility to make re-adjustments after the components have been located on the tooling.
U.S. Pat. No. 4,641,819 discloses programmable devices which are positioned accurately for the intended location of parts and which have locating means which, by their location, define the location of the part. Programmable devices, conventionally known as robots, locate the parts. The device of the '819 patent has a set of locator gross adjustment means, and a set of locator fine adjustment means.
U.S. Pat. No. 4,821,408 discloses passive positioning means, or a jig, with holding means that can be moved by separate moving means.
U.S. Pat. No. 4,738,387 addresses an assembly station layout, stacking of parts, and storage of parts.
U.S. Pat. No. 4,811,891 discloses a method of two-wheeled vehicle assembly. Jigs are fixed as typical with hard automation. The '891 patent does not teach flexibility in adapting to differences in body, or frame, size, or to components of different shapes.
U.S. Pat. No. 4,960,969 discloses a conventional use of robots for the transfer of panels when combined with tool changing to allow robots to handle as well as process parts, such as by spot welding.
U.S. Pat. No. 4,691,905 discloses forming the mounting face of a part holder to the "form" of the part.
French Patent Document No. 2631-100-A discloses a positioner that moves a part after it has been clamped to it.
U.S. Pat. No. 4,894,901 addresses cooperative processing of one part by two robots, one for holding and one for processing.
U.S. Pat. No. 4,875,273 discloses a device which positions parts by fixed jigs. A robot moves the composite assembly.
U.S. Pat. No. 3,624,886 relates to conventional hard automation and component assembly methods using same.
Prior art fixtures generally must be tailored to specific models, sizes, and styles of car bodies. Different fixtures are required for each subassembly even when variations are small between car body styles. It is therefore necessary to build multiple fixtures whenever more than one body style is to be manufactured in the same production facility. With the proliferation of body sizes and styles in the auto industry, it is obvious that this approach imposes appreciable cost penalties on automotive manufacturers in several ways:
Initial investment in multiple dedicated fixtures. PA1 Excessive demand on floor space to accommodate multiple fixtures, hence larger capital investment in plant buildings and facilities. PA1 Replacement cost of fixtures whenever new models are introduced. PA1 Idle plant capacity and lost sales opportunities whenever market demand shifts between car models; when idle capacity of low selling models cannot be readily used to manufacture hot selling ones. PA1 Low product quality, hence less profits, as fixture adjustment shifts with use. PA1 Inflexibility in accommodating design changes which may affect body location features, hence, less responsiveness to market demands and loss of sales. PA1 Flexible (i.e., accommodates a mix of body sizes, running design changes, and model changes); PA1 Economical (i.e., provides appreciable cost savings over current hard automation systems despite its added benefits for being Model independent, and usable across model changes); PA1 Efficient (i.e., gets tooling off the critical path of new model introduction programs, thus allowing faster new model introductions to the market, and quick retooling by program change instead of hardware fabrication); PA1 Accurate (i.e., provides improvements in tooling accuracy and tooling consistency through programmability and adaptive tuning, and requiring less dependency on human judgment); PA1 Consistent (i.e., always locates the body components in the desired location without manual adjustment, shimming, clamping, etc.; The location points do not change with frequent use); PA1 Automatable (i.e., allows the automation of all processes associated with automotive body assembly such as material handling of large and small components, and panel placement, location, clamping, and joining). PA1 (1) Provide programmable location and support points which can be adjusted depending on the size, height, and other features of the component (panel) to be received, supported, and located. PA1 (2) Receive the component within a space that provides high tolerance for component mislocation in position and orientation, hence, it allows the approximate location of the component by component delivery equipment, such as robots. PA1 (3) Adjust the component accurately to a desired location after the component has been received at an approximate location. PA1 (4) Sense the location of critical positioning features in space and provide necessary adjustment to the locators. This assures accurate location of critical positioning features relative to each other and corrects for part inaccuracies without affecting its intended function. PA1 (5) Clamp or confine each component in its desired location. PA1 (6) Allow for process equipment to partially join the components of an assembly, such as by spot welding or bonding, and maintain dimensional stability in preparation for further processing by other process equipment and complete joining. PA1 (7) Allow for processing equipment, such as material joining, removal, and fastening robots, to perform desired processes while the assembled components are accurately located. PA1 (8) Allow for the integration of process functions in common equipment, such as by using clamping tips for spot welding. PA1 (9) Allow for modularization of the manufacting process by integrating the fixtures with process tooling in one cell. Low volume manufacturing can then be done in limited floor space. PA1 (10) Allow for material handling of components through flexible automation, such as with robotic devices. Hence, provide opportunity for full automation of the manufacturing process with all associated benefits in quality, consistency and higher reliability and uptime of production lines. PA1 (11) Allow for the modularization of the location equipment, where the location and positioning devices can be all identical or made of common components; hence reduces cost, increases reliability and allows for ease of maintenance and service. PA1 (12) Can be configured for different components (panels) and transferred for use from one automotive model year to the next, or from one plant to another. For new models, only the spacial location of the modules on a platform may change to accommodate the new model geometry.
The prior art generally follows a "hard automation" approach. Very few tooling systems have the capability to accommodate more than one panel unless the variations between panels are minor and are not related to the critical location features of the tooling. Occasionally, tooling may be designed with additional features that may accommodate one or more different panels, but this adds to the complexity, cost, and size of the tooling; and also detracts from its reliability. An example is shown in U.S. Pat. No. 4,256,947.
Because of this rigidity in application, current hard tooling fixtures must be changed with each model change. This translates into long lead time requirements for the introduction of new models, higher production cost for automobiles, slow response to market demands for new features, and in general, unfavorable competitive position for the auto manufacturer.
Furthermore, hard tooling is subject to misadjustment as locators shift in place with continuous use and frequent impact on the friction-held locators. This results in poorly located parts and the need for frequent adjustment. Since the adjustment is done by shimming and bolt clamping, this is a tedious process that cannot be done precisely and results in inconsistency in tooling and poor quality in products.
In the prior art, material handling is usually done manually or by dedicated material handling mechanisms. Panels are placed in the fixtures manually and may require the cooperative effort of two persons, especially for heavy or flimsy (pliable) parts that require multiple points of support. This is a tedious operation which reduces product quality as people become tired and damage panels by misplacement, dents, and abrasion. Dedicated placement and transfer mechanisms also have limited use as they occupy a permanent location and cannot usually be utilized to automate all candidate operations because of conflicting space requirements. The cost and space penalties associated with automating the placement and transfer of small components does not usually justify its application. Hence, such automation is usually limited to large and heavy parts and subassemblies. Therefore, full automation is generally impractical with the prior art.